A motor driving device such as a servo amplifier is categorized, in terms of the method for processing regenerative power (energy) produced at the time of driving the motor, into a power-supply regeneration type in which regenerative power is returned to a power supply, and a resistance regeneration type in which regenerative power is consumed by a regenerative resistance (a regenerative brake). The resistance-regeneration-type motor driving device is different from the power-supply-regeneration-type motor driving device in that it is not necessary to provide a dedicated circuit that returns regenerative power to the power supply (such as a power-supply regenerative converter). Therefore, the resistance-regeneration-type motor driving device is more advantageous in that the hardware cost is lower than the power-supply-regeneration-type motor driving device, and has been widely used as a motor driving device for driving an industrial machine.
Meanwhile, there has conventionally been a demand for accurately gasping the power consumption when a motor driving device drives the motor without providing a costly dedicated measurement device such as a power meter. This is because grasping the power consumption accurately makes it possible to accurately identify electricity cost at the time of driving the motor, and to appropriately select the capacitance of power source facility.
In order to solve the problem as described above, Patent Literature 1, for example, discloses a technique for a resistance-regeneration-type motor driving device that is supplied with power from a common power-supply unit, and that drives a plurality of axes, in which a total value of outputs of the respective axes is calculated, and when the total value is negative, the power amount is considered as zero to calculate the overall power consumption. In Patent Literature 1, when the total value of outputs of the respective axes is negative, the power amount is considered as zero, and a process is performed assuming that the amount of power corresponding to this negative value is consumed by a regenerative resistance.